Scientifically, the term “glass” is used to designate any solid that possesses a non-crystalline (amorphous) structure at the atomic scale and exhibits a glass transition when heated towards the liquid state. In certain instances, glasses can be transparent. Glasses can be formed from oxides such as silicates (based on silica, also known as silicon dioxide or quartz), non-oxides such as chalcogenides, porcelains, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and thermoplastic polymers. On the other hand, a “ceramic” is an inorganic nonmetallic solid comprising metal, nonmetal or metalloid atoms primarily held in ionic and covalent bonds. The crystallinity of ceramic materials ranges from highly oriented to semi-crystalline, and sometimes completely amorphous (such as in the case of certain glasses).
Inorganic solids generally exist in a disordered glassy, a polycrystalline ceramic, and/or a fully ordered single crystal state. A transformation from glass to ceramic is achieved readily by heating the former to a particular temperature that inevitably leads to nucleation of many crystals. In producing a single crystal, the creation of multiple nuclei must be avoided. For this reason, most single crystals are produced by liquid-to-solid (not solid-to-solid) transformation, in which formation of extraneous nuclei during the growth of the initially formed nucleus is unstable in the surrounding liquid phase.
However, there are serious drawbacks of single crystal growth from melts. Such methods are not useful for fabricating crystals of compositions that decompose, transform to some undesirable phase, or melt incongruently on heating. Consequently, it is extremely difficult or impossible to grow single crystals of many complex oxides, such as high Tc superconductors, and organometallic halide perovskites for solar cells of exceptional efficiency. This lack of high quality crystals is identified as a critical limitation to the progress of materials by design paradigm. For these materials, elevated temperatures and melting need to be avoided.
The concept of glass-to-single crystal transformation has not been achievable in the art due to concurrent nucleation at multiple sites, which ultimately produced polycrystalline glass-ceramic instead of single crystal. Attempts to implement a single crystal architecture in glass (SCAG) fabrication using continuous wave (CW) and femtosecond (fs) lasers led to formation of a single crystal during cooling of molten material that is produced in the vicinity of the laser focus. This process does not have the desired advantages of a solid-state transformation of glass-to-single crystal, and very much resembles the traditional floating zone crystal growth from the melt.
There is thus a need in the art for novel methods of promoting single crystal growth via solid-solid transformation of an appropriate glass. The present invention addresses this need.